1. Field of the Invention
This invention relates to a steering damper device for a motorcycle for attenuating oscillations of its handlebar during running operation, and more particularly a device capable of making a damping force variable.
2. Description of Background Art
In order to prevent any oscillation of a handlebar caused by a kickback or the like under external disturbance, it is well known in the art to provide a steering damper device generating a damping force against oscillation (as one example, refer to Japanese Patent No. 2,593,461). In addition, it is also well known in the art to provide a device generating a damping force only when it is required and making a damping force variable in other cases so as not to generate any surplus damping force. Examples include a device for controlling it in response to a steering angle and a running speed (refer to Japanese Patent Laid-Open No. Sho 63-64888), and a device for controlling it in response to a variation in a load of the front wheel (refer to Japanese Patent Publication No. Hei 7-74023).
As disclosed in Japanese Patent Publication No. Hei 7-74023, when a front wheel load is decreased, a kickback phenomenon may easily be produced, and either an inner pressure at a front fork or its stroke in this case detects the decreased front wheel load. However, usually a pressure in the front fork is changed in response to its inner temperature, making it difficult to perform an accurate sensing of the front wheel load. In addition, when the stroke of the front wheel is detected, the structure of detecting the stroke becomes complicated and the cost required for the entire vehicle body is increased. In view of this fact, it is desired to detect the front wheel load by a more accurate and simple detecting structure.
The present invention addresses the problems described above. In order to solve the above problems, the steering damper device of the present invention produces a damping force applied to a turning operation of a front wheel steering system supported at a vehicle body front segment. The value of the damping force is made variable, wherein an acceleration sensing means for sensing an acceleration of the vehicle body is provided, and only when the acceleration exceeds a predetermined threshold value, is the damping force generated at the steering damper.
This makes it possible to generate a damping force at the steering damper only when both a speed of the vehicle body and an acceleration of the vehicle body exceed the predetermined threshold values. In addition, it is also possible to cause the damping force of the steering damper to be changed in response to a speed and/or an acceleration of the vehicle body.
Further, it is also possible to detect a speed of the vehicle body in response to a gear position and the frequency of rotation of the engine, and to detect an acceleration of the vehicle body in response to an opening speed of the throttle.
In accordance with the present invention, when an acceleration of the vehicle body exceeds a predetermined threshold value, the load on the front wheel is decreased. When this occurs, a kickback may occur. However, with the present invention, it is possible to generate a damping force at the steering damper and to restrict the kickback. Further, with the present invention, since an acceleration of the vehicle body is not influenced by a temperature, detecting the acceleration is not as difficult as is the case with prior art devices. Thus, since a complex structure for use in detecting the acceleration is not required, the present invention provides for a more accurate and simple damping force control.
If in addition to the acceleration, the vehicle body speed is also applied as a controlling condition, a damping force is generated only when the vehicle body speed exceeds a predetermined threshold value. Thus, the controlling operation preventing against kickback becomes more accurate. This state is attained based on the fact that a relative large acceleration is apt to be generated at a low vehicle speed, and a relative low acceleration is apt to be generated at a high vehicle speed. Thus, by also considering the vehicle body speed as well as the acceleration, the present invention provides a means for correcting the damping force generated only by the acceleration.
Further, if the damping force is changed in response to either a vehicle body speed or a vehicle acceleration, or both of them, it is possible to generate an appropriate damping force of the steering damper responding to an operating state.
In addition, when a vehicle body speed is detected in response to both a gear position and the engine rotation frequency and an acceleration is detected in response to a throttle opening speed, it is not necessary to use an acceleration sensor or a vehicle body speed sensor exclusively. When both the vehicle body speed and the vehicle acceleration are considered, an appropriate damping force of the steering damper can be more accurately generated.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.